Acetophenone



Patented Mar. 27, 1945 ACETOPEWONE William S. Emerson, Van Buren Township, Montsomery County, Ohio, assls'nor to Monsanto Chemical Company, a corporation of Delaware pnlication August as, 1942,

Serial No. 456,533 seams. (cl. zoo-592 This invention relates to a method for the preparation of acetophenone from alpha-chlorostyrene.

In the preparation of aeetophenone the methods followed heretofore have been based particuiarly upon the Friedel-Crafts reaction, involving the condensation of benzene with acetyl chloride, acetic anhydride, various acetates or ketene in the presence of metal halide catalysts, espe- Such methods have cially aluminum chloride. been characterized by high catalyst costs, the employment or molecular'equivalents of, for ex ample, aluminum chloride, being essential in the Friedel-Crafts synthesis of ketones and the recovery oi such catalysts in the desirably anhydrous state being impracticable. Acetophenone has likewise been prepared by a variety of other methods. butthe prior processes have been of little industrial interest in that they have been characterized not only by high costs but also by uncertain yields and atttended with various other diiflculties. For example, it was long ago known to heat alpha-chlorostyrene with concentrated hydrochloric acid to a yield a mixture of tri-- phenylbenzene and acetophenone (A. Behal. Bull. soc. chim. (2), 637, (1888l). Ina further experiment recorded in the literature a good yield of acetophenone was obtained by boiling for three hours a mixture of chlorcstyrene with more than 3 times itsjamount by weight of concentrated hydrochloric acid-(E. Eden and L. Namias. Bull.

@506. chim. (5),.3, 2336 (1938)). This method is costly because under the reaction conditions it is impossible to prevent voiatilizaticn and consequent dissipation of the concentrated hydrochlorlc' acid. Moreover, the difiusion o! the volatiliaed hydrosen chloride throughout the reaction equipment causes considerable corrosion; so

that the principles here involved never led to any 49 practicalapplication. I V

I have attempted the conversion. of alpha chlorostyrene into acetophenone by employins various dilute concentrations of hydrochloric acid inmoithcstronzacidlnordertoelimmu corrosion problems and loss or hydrogen chloride. However. the use of such diluted hydrochloric acids resulted in only negligible yieidsor aceto- Thepresentinventionishasedonthediscoveryw that certain concentrations of sulfuric acid. within narrow limits, give improved yields oi acetoature facilitating a steady and non-violent evolution of hydrogen chloride, i. e., at 30 0. results the reaction equipment under the reaction condi time.

As anoleilnic, unsaturated compound, alphachlorostyrene would be expected to be adversely affected by sulfuric acid; that is, either char-ring,

.sulfonation, polymerization or oxidation would,

be expected to precede and prevail over the reaction involving the conversion of alpha-chlorostyrene to acetophenone. As a matter of. fact, unless reaction conditions as herein defined are carefully adhered to, only heterogenous prod-.-

-ucts are obtained by reaction or alpha-chlorostyrene with sulfuric acid.

When alpha-ohlorostyrene is heated with apll proximately 5 timesits weight of 80% aqueous sulfuric acid, 1 obtain a good yield of acetophenone; however, when I increase the concentration of the acid to 85%, the yield of acetophenone is reduced to about 01 that secured 80 with the 80% aeid. Likewise. when I employ a concentration of the acid instead of the acid, I obtain a similar reduction in yelds.

The present invention is illustrated by the following example:

Add 20 g, of alpha-ohlorostyrene to 100 g. of a cold, substantially 80% aqueous solution or sulfuric acid. Warm the resultins mixture to 3-.

temperature of about 60 0., and allow it to remain at this temperature until the evolution 01' hydrogen chloride has ceased, generally requirinz approximately 5 hours. Extract the productbenzenesextract unwith benzene and distil the der partial vacuum. 14 g. (81% yield oi-ace 'phenoneisrecovered.

The use of an 85% suliurieacid at a temperin the production of a 46% yield 0! scstophen when I employer weaker acid, I preferably co hisher temperatures. with 75% sulfuric acid at temperatures or irom 80 C. to

'. c. I obtain a 54% yield of acetophenone.

On the other hand. with 96% suliurieacid, cr-

dinary' rooin. temperature or even lower temperatures are advantageously used in order to avoid Hence. while 1 m me at acid concentrayieldsotacetophenonelprefertoempioy con ttations of 1mm, say-78% to 82%.

can whenusinsacidswithinthisransooieoncentra- -flon1havotoundtinttcmneramres also O.to

m m s s onotcongsivstol ea c. are advantageously cm ic c 'tnarmso with 96%.suliuric acid. thereis a de-' crease in yield, only 23% of the ketone heinsobv lence.

of temperature being conducive to a steady, smooth evolution of reaction hydrogen chloride and the formation of maximum yields of acetophenone in the shortest time. Lower temperations 01' acid, and likewise the lower temperatures withthe higher concentrations of acid.

What I claim is:

1. A process which comprises reacting alphachloro-styrene with sulfuric acid of from approximately '78% to approximately 82% H2804 content and controlling the temperature of the reaction within the range of from approximately 55 C. to approximately 65 0., the higher temperature corresponding to the lower acid concentration and vice versa.

2. A process which comprise reacting alphachloro-styrene with sulfuric acid of substantial- 1y 80% H2304 content while maintaining the temperature at a point to cause a regular and non-violent evolution of hydrogen chloride.

7 WIILIAM SEMERSON. 

